This invention relates to wound-healing dressings and to methods for enhancing the quality of wound healing. In particular, the invention relates to the healing of corneal wounds. In one embodiment, the invention relates to methods and materials for improving the results obtainable in keratorefractive surgeries, such as radial keratotomy, by altering the course of healing of the surgical incisions. In another embodiment, the invention relates to the sutureless closing of tears or perforations of the cornea, limbus, sclera and all oculoplasty.
As used herein, the term "wound" includes surgical incisions as well as wounds caused by accidental trauma or disease. A considerable body of literature is devoted to methods for improving wound-healing, both in terms of increasing rates of healing and avoiding undesirable effects associated with natural wound-healing processes, such as scarring and contraction of healed tissue. Not only are those effects undesirable from a cosmetic point of view, but also, in the case of corneal wounds, they can interfere with visual function.
U.S. Pat. No. 4,453,939 to Zimmerman et al. discloses a composition and its use for sealing and healing of wounds. The composition comprises a collagen carrier which is coated on one or all faces with a mixture of a fibrinogen component which contains fibrinogen, factor XIII-containing fibrinogen or a mixture thereof, and a thrombin component. It is said that the mixture may contain additives, such as fibronectin which promote the infiltration and growth of fibroblasts. Those skilled in the art are aware that the deposition of collagenous materials into a wound bed may have undesirable effects in wound healing, since crosslinking of collagen during the healing process tends to cause tissue shrinkage and scarring. These effects are particularly undesirable in ophthalmological applications, where scarring and shrinkage may impair vision. U.S. Pat. No. 4,444,787 describes the treatment of wounded ocular tissue by the topical application of collagen crosslinking inhibitors to the tissue. Application of the crosslinking inhibitor is said to reduce shrinkage of collagen fibers located in ocular tissue.
A number of publications describe the use of tissue adhesives to bind wound surfaces following accidental corneal perforations or corneal surgery. These include: Ophthalmic Surg., 15(1):55-57 (1984); Aust. J. Ophtalmol., 11(2):113-118 (1983); Opthalmology, 89(6):630-635 (1982); Ophthalmic Surg., 13(6):475-477 (1982); Opthalmic Surg., 10(3): 58-64 (1979); J. Biomed. Mater. Res., 5(1):113-119 (1972); Trans. Pac. Coast Ophthalmol. Soc., 50:12-125 (1969); Trans. Am. Acad. Ophthalmol. Otolaryngol., 73(3):499-505 (1969). The most commonly employed adhesives for use in healing wounds of the eye are cyanoacrylate type adhesives.
An adhesive of choice for treating corneal perforations is currently cyanoacrylate. Disadvantages of cyanoacrylate are that the perforation has to be completely dry before application; the polymerized glue may present brittle edges that further irritate the eye; and the glue is not sterile and is not readily available in an acceptable delivery system for the sterile field.
Wound healing in keratorefractive surgeries, such as radial keratotomies, presents an entirely different set of problems and objectives by comparison with the healing of traumatic wounds, such as corneal perforations. In the case of traumatic wounds, such as corneal tears or perforations, the desired objective is to restore the wounded tissue as nearly as possible to its original configuration. In keratorefractive surgeries, however, incisions are made into the cornea for the specific purpose of permanently changing the geometry of the cornea. Restoration of the tissues to their original configuration, therefore, would tend to reverse the desired effects of the surgery.
Keratorefractive surgeries are intended to correct vision problems caused by defects in the geometry of the eye by surgically altering the corneal geometry. Radial keratotomy is a keratorefractive surgical procedure which is employed to correct myopia caused by excessive corneal curvature. In this technique, a series of incisions is made in the cornea, usually penetrating about 90 to 95% of the thickness of the cornea. The incisions, extend along lines which radiate outwardly from the corneal center. The number of incisions may vary from as few as four to as many as 16, with 8 to 12 being commonly employed. The incisions allow the cornea to relax and to flatten out somewhat, thereby reducing or eliminating nearsightedness. Similar procedures, in which corneal incisions are made in directions other than radial directions, have been employed to correct some astigmatisms.
While radial keratotomy and related keratorefractive surgeries have become fairly commonplace, the results achieved using presently available techniques are not highly predictable or controllable in any given patient. In particular, the degree of correction is not well controlled and may be more or less than is needed by the particular individual, so that the operation may have to be repeated or corrective lenses may still be needed. Furthermore, the healing process usually takes from 12 to 24 months, during which time some patients experience instability in visual acuity; that is, the cornea begins to reacquire some of the curvature lost as a result of the operation. Maximum flattening of the cornea usually occurs about 2 days after surgery, with a gradual increase in curvature occurring thereafter until the incisions have healed.
Some keratotomy patients have also encountered postoperative vision problems related to scarring. In some instances, scars at the healed incision sites cause light to be reflected within the eye, resulting in a perceived glare, particularly at night. Fluctuations in visual acuity throughout the day may also result.
It would be highly desirable to develop methods for maximizing the degree of corneal flattening obtainable in radial keratotomies as well as providing for a predictable degree of vision correction. Furthermore, it would be desirable to enhance the quality of healing of radial keratotomy incisions so that scarring would be minimized and to increase the rate at which healing occurs.